Not sure what you mena by 'Access Code'. If you means the code for an XP install, you will find it on the Microsoft sticker on your PC or CD. If you do not have a sticker your XP is pirated and you can't be helped here.
If I have this wrong please open a new post with (lots) more information.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix desktop pcs.